In a mixing bowl, combine the boneless chicken thighs with gochugaru, minced garlic, black pepper, gochujang, soy sauce, and sweetener. Massage well into the meat and let it marinate for about 10 minutes.

Bring a large pot of water to a rolling boil and add the Korean instant Ramyeon noodles. Cook for 3-4 minutes, until slightly undercooked. Drain and set aside.

Heat a non-stick pan over medium-high heat with a splash of neutral oil. Add the marinated chicken pieces in a single layer and cook for 2-3 minutes on each side until golden brown.

Push the chicken to one side and add sliced onion and mixed mushrooms. Sauté for 2-3 minutes until tender and fragrant.

Add the drained noodles to the pan, tossing well with the chicken and vegetables for 1-2 minutes to absorb the juices.

Sprinkle shredded cheese over the noodle mixture and cover the pan with a lid. Reduce heat to low and let it melt for about 3-4 minutes.

Once the cheese is melted, scoop the cheesy chicken noodles into serving bowls and enjoy!